Applicator for radio-frequency heating



March 13, 1951 w. N. PARKER APPLICATOR FOR RADIO-FREQUENCY HEATINGV 2 SheeS-Shee 1 Filed April 50, 1948 n n mii i/YDE 545679055 ///////1'KlldKlm) Gew-amn:

MMM/J7 c/W/r/ dir/rf 616/0 FLICIODE NVENTOR WILLIAM N PARKER ATTO R N EY March 13, 1951 Y w.` N. PARKER APPLICATOR FOR RADIO-FREQUENCY HEATING 2 Sheets-Shee 2 Filed April 3G, 1948 INVENTOR WILLIAM N. PARKER ATTORNEY Patented Mar. 13, 1951 APPLICATOR FOR RADIO-FREQUENCY HEATING William N. Parker, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application April 30, 194.8, Serial No. 24,380

1 The present invention relates to R.-F. heating f'applicators for bodies of dielectric material and E the like, and more particularly to a radal cavity V'type of R.-F. heating applicator which is adaptlfed to heat continuous long threads or cords of dielectric material, such as rayon yarn and the like.

Because of the relatively small cross sectional 'area and the lamentary nature of threads and cords of dielectric material, the applicat'on of R.F. heating thereto in the manufacture or quantity production of such materials presents a iiihcult problem. High frequency power of the order Aof hundreds of megacycles must be generated and the worlr material must be passed 'through a highly concentrated electrical iield. ,Such material can best be processed in a contnuously moving cord or bundle'of fibers, however, the slow rate of travel through the electric 'eld v`heretofore available has involved considerable Iproduction time and cost.

It is, therefore, a primary object of this inven- ,Ition, to provide a simplified and effective method and means for heating filamentary bodies of di- 'electric material, such as rayon yarn, at a relatively high rate of speed in a highly concentrated Yelectrical field through electrical means including an oscillator system which is highly stable in response to variation in load imposed upon it by the work, for example as the moisture content varies `in the dielectric body being processed.

It is a further object of the invention, to provide an improved R.-F. heating applicator system comprising a radial cavity resonator having means at the axis thereof for concentrating a electronic tube.

In accordance with the invention, the radial length of the main cavity through the axis of' Vwhich the material is passed, is substantially of order of one half wavelength of the frequency f to"which the system vis responsive and the gridanfode and grid-cathode cavities are located ra- 'dially externally of the tube elements although being rigidly coupled so that the system oscillates as one circuit with a nearly constant feedback ratio. The resulting stability as the electronic -tilbe or oscillator is loaded provides a distinct ad- 6 Claims. (Cl. 21B-47) vantage over the usual high frequency oscillator which depends upon feedback loops and relatively Weak couplings by the resonant circuits. 1

It may also be considered to be an important object of the invention to provide a radial cavity high frequency R.F. heating applicator for dielectric heating and the like of improved construction, comprising a closedradial cavity system operating in such a mode that a relatively high and concentrated electrical iield is established at the center or axis through which the work is moved or located for treatment, together with active electronic tube oscillator elements symmetrically disposed in a disc-ring arrangement of relatively short radiusabout the axis. of the cavity substantially at the periphery' thereof and in a zone of electrical fields of the proper phase and amplitude for the generation of high frequency power, whereby such power may be'applied directly to the work in the cavity. 'j

More generally, also, it is an object of this invention, to provide an improved high frequency R.F. heating applicator system for the heat treatment of moving bodies of dielectric material such as rayon thread and cords, either singly or in multiple, which utilizes a closed resonant cavity and a closely coupled electronic tube structure of the disc-ring type whereby the applicator structure is compact and simplified in construction and of low cost in manufacture.

A further and more specific object of the invention is to provide a totally enclosed high frequency R.F. heating applicator comprisingsimple and improved means for generating and applying R.F. energy to work being processed by dielectric heating, such as rayon yarn for example.

In carrying the invention into effect, the work to be heated is located at or passed through the center of a circular radial resonant cavity joined at its outer periphery 4with two other radial cavities in substantially parallel relation, in such'- a manner that the proper R.F voltages exist on a disc-ring active tube structure located substantially at the junction zone of the cavities, whereby the tube elements and the cavities coupled therei by operate as a single oscillatory systemfor applying high frequency R.-F. energy to thework Yat the center of the main cavity.

ing description when read in connection with the accompanying drawings, in which Figure l is a view in elevation and in cross section, of an R.-F. heating applicator embodying the invention,

Figures 2 and 3 are diagrammatic representations also in elevation and in cross section, on an enlarged scale, of portions of the structure shown in Figure 1, illustrating certain principles and modes of operation of an applicator system embodying the invention,

Figure 4 is a view in elevation and partly in cross section, of an R.-F. heating applicator embodying the invention, being a modication of the system shown in Figure 1, and

Figure 5 is a plan view of the embodiment of the invention shown in Figure 4.

Referring to Figures l, 2 and 3 in which likeV parts throughout are indicated by like reference ""numerals, two cylindrical or circular flanges casing members It and II are mounted one on the other in registering face to face relation to pro- Avvde 'a hollow interior comprising a centralradial cavity I2 and two circular annularcavities 'i3 tric insulating material. rIhe ilanges l5 and iii are of short radial Width, whereas the rings I1, I8 and I9 are of greater Width, extending in.- wardly of the casing to a greater radial depth.

The conducting ring I1 projects beyond the in- I sulating rings I3 and I8 for the purpose of providing a connection with an annular electronic Y tube structure which is interposed between and I coupled with the cavities I2, i3 and I4.

The electronic tube structure is of the discring type comprising an annular ring anode element 2| adjacent the casing element iii and separated from the interior wall thereof by a suitable insulating dielectric plate 22 in the form of an annular flat ring, and annular ring-like cathode electrode structure 23 seated on and secured to the interior wall of the other casing element il in spaced opposed relation to the anode electrode, and a thin annular grid element 24 interposed in the space between the anode and cathode elements and having a thin walled perforated active grid section 25 directly between the anode and cathode elements.

The grid ring is seated on and connects with the annular ring I'I which forms the electrical output connection therefor, being uniformly symmetrical about the axis of the chamber I2 as are the grid electrode 25.

also the electron tube elements. The cathode structure 23 is trough-shaped in cross section, as indicated7 and is closed hermetically and sealed by a glass seal 26 to enclose a primary toroidal Y winding 21 from which it is energized inductively.

The active cathode element of the cathode structure is a thin heated annular channel member or ringA 2B which completes the single turn secondary yand forms the hot cathode surface adjacent 'to Both windings are annular in form as shown, and the primary winding is energized from a suitable alternating current source through input leads indicated at 28. Any

. other suitable cathode structure, however, may

be provided.

A"The active elements of the electron tube are contained in an evacuated envelope which in the present example is provided by inner and outer annular ring walls or wall elements 32 and 33 coaxial with the chamber I2 and the active electrode elements, being spaced on opposite sides of the anode element 2| and between it and the grid ring 24. rlhe tube casing or envelope is completed by a second pair of annular ring-like Wall elements 34 and 35, positioned about and concentric with the annular cathode. The side Wall elements of the tube structure may be of any suitable material providing high dielectric insulation between the tube elements and serving to seal the envelope. For example, the side wall of the tube may be of glass sealed to the cathode and anode which `are iianged for the purpose and to the grid ring as shown in Figure 1.

With this arrangement, it will be seen that the cathode electrode is grounded tothe casing liJ-I I `which is also of conducting material, whilemthe anode electrode is insulated from the casing'and provided with an input connection lead'` 3] through which positive operating potentials are applied. The tube structure receives a'biasng potential through a connection lead 38 connected with the central annular ring Il lwhich in tur'h contacts with the grid ring 24 whichisseated thereon. *Y l f The center of the high frequency applicator-is provided with central registering openings `r ports 4H and 4l in the casing elements Ii! `andi I respectively, directly at the center of the resonant chamber I2, and the openings are internally prvided with surrounding inwardly projecting boss'e's 42 which operate as electrodes between which high voltages are set up by operation of thetubje, as will hereinafter be described to establish a concentrated electrical eld at the center oraxis of the cavity. The openings 40 and 4I are of suiicient size or diameter to permit the passage therethrough or the work to be heated, which in the present example is represented as a single enlarged cord of dielectric material or other work material, such as rayon, which is to be treated by heat as it passes in a continuous thread through the apparatus. The direction of movement is indicated by the arrow, although itfis reversible. The annular electron tube structure is arranged to lie at the periphery or boundary of theannular chamber i2 and separates the latter'chamber from the annular chambers I3 and I4 at the outer periphery of the casing. The chamber` I3 is so proportioned that it provides a resonant grid-anode cavity, while the chamber I4 is so proportioned that it provides a resonant gridcathode cavity for the electronic tube, Vwhile the radial chamber i3 provides an anode-cathode cavity or load for the electronic tube.

The three cavities are coupled through the tube structure which lies at the junction of the three cavities, and the tube is operated oroscillates in operation, to provide zones of high potentialpr strong electrical fields' at the electrodesgliZigand :within its tube structure, while the zones ofweak electrical iields fall within the cavities I3 and.;!4 and midway radially ywithin the cavity I2.`r This condition of operation is obtained by making the disc-rings 2 i, 25 and 23E-9, or tube elements, of an average radius approximately equivalent to an electrical half wavelength in the radial cavity I2, which forms the anode-cathode load circuit as above noted. Under these Yconditions t h e'SEL-ill'. oscillations in the cavity I2, when the' tub'eis ausg-16o "'rlergized, will .set up Vzonesnoj strong electrical field at the tube elements and near the axis of the annular structure. The field will tend to become 'considerably greater at the center due to the high surge impedance at this point, which is a desirable feature inherent in radial cavities which is used to advantage in the structure shown.

, The moving rayon yarn cord 43 to be treated is thus exposed continuously to .a strong electrical eld and will, therefore, absorb a maximum of energy. Furthermore, this loading is uniformly distributed on the active tube elements due to the inherent symmetry of the structure.

The essential elements. of the structure-of Figure 1 are diagrammatically indicated in Figure 2, wherein thesimpliedoutline of the structure may provide a better understanding of the relation of the cavities and the coupling provided therebetween by the tube structure. Referring to Figure 2 along `with Figure 1, it will be seen vthat the cathode, grid, and anode elements of the tube in annular form, are interposed between the .radial central chamber I2 and the annular chambers lI 3 and I4. The disc-ring type of tube structure shown is thus combined with a closed radial cavity type oi applicator in such a .manner as to provide a self-exciting oscillator and to provide a concentrated electrical eld at the center of the structure through which the work material passes f radially.

. As indicated furtherin Figure'z, the work mal terial .may comprise a plurality of threads 4'5 and ,Y 46 of dielectric material as indicated arranged in any suitable manner to pass through the openings .40 and 4I which likewise may be made of a size to suit the number of threads forming the wor to be heated.

The Zone of high electrical stress at the center of the cavity i2 may further be conned to the .area about the moving work by electrode elements 4..41 and 45 o1" dielectric material arranged as inwardly projecting tapered rings surrounding the of the structure of Figure 2 is shown in a further diagrammatical manner with enlarged spaces between the grid electrode and the anode and the cathode, in order to maintain an eilicient oscillating condition, it is necessary that the cathodegrid voltage be a certain fraction of the cathode-V Y anode voltage and substantially 180 out of phase* l.vlith it. ,This condition is insured by proper tun-- ing of the grid-anode and the grid-cathode cavities located outside the annular or vdisc-ring tube elements. .Fligure 3. .shows the .junction of fthe,V lthree resonant cavities I 2, I3`and .I4 taking place n at the free end or inner .edge of the `grid electrode. The three resonant circuits are effectively connected in series so that the sum of the three junction voltages must be zero. vIn order that the cathode-gridand cathodej; anode voltages maybe out of phase, the impedyances at A and B, which the anode-grid cavity looks into, must have the same kind of reactance, and a ,ratio A/B equal to the desired feedback fvoltage ratio.

If A- andB are made capacitive by making the grid-cathode and anode-cathode cavities appropriate electrical lengths, the operation will be similar to the usual well known Colj'fpittsoscillator circuit. '-The grid-anode cavity *must* in this case actas the'st-ank -inductance.- #If- 6 desired, A and B maybe made inductive and the grid-anode cavity capacitative.

Since all three cavities arerigidly coupled'together, they oscillate eiectively as one circuitat the frequency determined approximately by the radial length of the cavity I2, with a nearly-constant feedback ratio, similar to a lumped constant Colpitts circuit. The resulting stability as Vthe oscillator is loaded by the presence of work material passing through the cavity with varying degrees of moisture content, gives the device of the present invention a considerable advantage over known high frequency oscillators which depend upon feedback loopsand relatively weak couplings between the resonant circuits.

It is to be further understood that radial cavity I2 may be operated at higher order modes and still fulll the condition of strong axial electric elds at the center and at the electronically active elements 2i, 23 and In this case the radius 0f cavity I2 is chosen to be substantially an integral number of electrical half-waves in accordance with well known radial cavity design procedure. Likewise, cavities such as I3 and I4 for providing feedback may be operated at higher modes as long as the respective input impedances at the junction of the various cavities Jiulll the conditions for self-oscillation as previously discussed.

The Work load may best be exposed to the most central region of high electric iield. However, any of the concentric high electric eld regions may be used for'this purpose. Furthermore, the

positions relative to the axis of cavities I3 and i4 and cavity i2 may be interchanged within the scope oi the'invention. 1

In the actual tube structure as shown in Figure 1, it Will be noted that not only must the active tube elements be enclosed in an evacuated chamber, but also certain blocking capacitors vmust be inserted to maintain the proper D.C. voltages on the grid and the anode with respect to the cathode. In the present example, suitable plate and cathode blocking capacitors are provided by the presence of the dielectric material 22 between the anode 2l and the casing wall, and likewisethe desired grid blocking capacitor is provided by means of the ceramic rings I8 and I9 interposed between the casing and the grid supporting ring I'I.

Likewise, it Will be seen that at the center of the cavity the projections or electrode tips 42 of Figure 1 and the electrode tips 4i and 48 of Figure 2 of high dielectric ccnstant'low loss insulating material, serve to concentrate thev electrical i'ied in the moving work being treated. For the same reason that a high voltage or strong electrical iield exists at the tube element, the body of the tube structure comprising the side walls 32,' 33, -Stand 35 should be of low-loss insulating material.

From the foregoing description, it will be seen that a structureA in accordance with the invention provides a simple and improved means for generating and applying ift-F. energy to work being processed by dielectric heating, such as rayon yarn or any long,fcontirluous"lamentary body, and that the'` work'to be heated may be' located at or passed axially through the center Voit" a simple circular radial cavity. 1t is essential, however, thatrthe cavity be coupled at its outer periphery to` two other radial cavities 'in suchv a manner that the proper R.F. voltages exist in the v' disc-ring oscillator tube elements locatedY substantially at thejunct'ionzone--oi the cavities.

` pOWeI'.

power. :out vappreciable loss directly to the work as it passes through the central cavity.

-vinternal flanges I and I6.

-As will be seen with reference to Figure 3 particularly, the grid-anode cavity may be electrically .short in order to operate as the tank inductance at the periphery thereof and located in a zone of strong electric elds of the proper phase and amplitude for-the generation of high frequency Accordingly this power is applied with- Referring now to Figures 4 and 5, wherein like reference numerals are applied to similar parts as in Figures 1-3, the annular casing comprising the two complementary sections It and I I, provide a grid supporting annular flat ring I'I located between annular internally extending ianges I5 iand I6 and separated therefrom by suitable ceramic insulating annular discs I8 and le as in the preceding embodiment.

The casing islikewise provided with an internal central radial chamber I2 and outer peripherial annular chambers I3 and I4 constituting respectively the anode-cathode tuning cavity, the grid- .anode tank circuit cavity and the grid-cathode f cavity for a seriesof electron tubes Ell-55 inclu-` 5 sive, arranged in a circular configuration and equallyspaced about the center of the structure,

The tubes are located at the boundary of the junction of the cavities I3 and I-l with the cavity I2 as in the preceding embodiment, and function in a similar manner to apply high frequency en ergy to .a work load comprising, in the present s example, a body 56 of ceramic material toY be 'ftreated located on a pedestal 5l within the chamber I2 at the center thereof. A removable cover plate 58 in the casing section lli directly in registration with the pedestal 5l is provided for the removal and placement of the material to be t treated.

The electronic tubes 55-55 may be of the triode type having an anode sleeve 6I), a grid ring 6I "and a cathode terminal end 62, the latter being gseated in suitable socket element 63 connected lto or integral with the casing section I l for providing a direct ground connection therewith The grid rings 6I are arranged to engage the in- A ner edge ofthe grid connecting ring I'I for req ceiving controlling D.C potentials therefrom, and the grid blocking capacitors are provided as befor e through the medium of the ceramic rings I8 and I9 interposed between the ringv I'I and the The anode terminals Si! of the tubes are seated in split cylindrical contact sleeves 65 which in .turn pass through the top of thecasing Ill` and are joined to an annular flatring Ifv supported fromvthe casing. In this arrangement, fthe sleeves 65 are spaced from the casing to prevent grounding thereto and are electrically insulated therefrom through the medium of an annular 'v hat ring of insulating material 51 located between the rings 66 and the inner wall of the casing section I0. .f-pacitor as in the preceding example, and D.C. .,:.-a11 Qfle Qneratng. potentials are applied tothe.

This provides an anode blocking castructure.

anodes .through connectionsl leads. 31, which.

, f In the -arrangement shown, the electronictubes are of a more conventional disc-seal typeof triode, and as shown, several of such triodes may be mounted in a circle about the central axis .of the radial cavity for high frequency operation, and may be operated in parallel or may be connected to operate from any suitable alternating current source. In the case illustrated in Fig. 5, the tubes 5I and 54, for example, may operate on phase l, tubes 52 and 55 may operate on phase 2, and tubes I50 and 53 may operate on phase 3 oi a 3 phase power supply as indicated by the dotted connections in Figure 5. In thisjmodication, while the work 56 remains fixed inside the cavity until processed, it

is obvious that a central aperture may be proarrangement as described and as used in the embodimentshown in Figures 4 and 5, provides a relatively higheroutput and the enclosed type of circuit prevents a considerable loss of power by radiation. Furthermore, as inthe preceding embodiment, the resonant cavities are direc t fly coupled by the tube structure located between them at thecavity junction which is arranged to be in a Zone of high electrical stress, and the resultant radio frequency power is directly applied .to the vwork within the cavity.

tube arrangement of Figures 4 and 5 combined with a closed radial cavity type of application wherein the cavity radius is of the order of one half wavelength, provides a self-excited oscillator and a concentrated field in the center for the processing of any work material located or passed through axially. It should be noted that in this embodiment, the disc-ring elements are relatively short .radially and that the load provided by the work is uniformly distributed over the active tube elements, due to the inherent symmetry .of `the Because of the advantages of the simpleappli- Vcator arrangement in accordance `with the ,in-

,vention, the problem of applying effective R'.."F.

heating to a moving body of ceramic or other andthe invention is of present extensive usefulness inthe heat-"treatment of long lengthsof rayon yarn and the like in a continuouslymoviig ;,Casing hevigeA e central radial, ,Cavity 391e@ et production line.

Because of the highheat concentration the speed of production or movement of the yarn through the applicator may be greatly -increased and a plurality of threads mayjb'e heated simultaneously, f

I claim as my invention: 1. An R.F. heating applicator comprisinga its outer periphery by two substantially parallel radial cavities of annular form, an annular discring electronic tube oscillator located at the junction of said cavities, said central cavity being of a radial length of substantially an integral number of half wavelengths, whereby said cavities are resonated to provide a concentration of R.F. power at the center of said structure and of said central cavity, and means providing electrodes at the center of said central cavity for applying R.F. energy to a Work load.

2. An R.-F. heating applicator as dened in claim 1 wherein means are provided for passing a continuous body of dielectric material axially through the axis of said central chamber between said electrodes.

3. An R.F. heating applicator system comprising in combination, a radial cavity resonator having electrodal means at the axis thereof for providing a concentrated electrical eld, means for passing work material to be treated axially through said cavity resonator between said electrodal means, electronic tube oscillator means oi circular conguration located about the periphery of said cavity resonator, and means providing grid-anode and grid-cathode cavities radially externally of said electronic tube oscillator means and coupled therethrough to said rst named radial cavity resonator.

4. An R.F. heating applicator system as defined in claim 3 wherein the radial cavity resonator has a radius substantially of the order of one half wavelength of the frequency to which the system is responsive, and the electronic tube oscillator means is of the disc-ring type,of relatively short radial length.

5. An R.F. heating applicator for dielectric heating and the like, comprising a substantially closed casing providing a central radial cavity and an annular disc-ring electronic tube having grid anode and grid cathode coupling means dening the outer periphery of said central radial cavity for establishing a relatively high and concentrated electrical eld substantially at the axis of said cavity and at the active elements of said electronic tube, and means substantially at the axis of said cavity for receiving dielectric material and the like to be processed by R.F. heating within said casing.

6. A high frequency R.F. heating applicator comprising in combination, a cylindrical casing, an annular electronic tube structure of the discring type in said casing spaced substantially one half wavelength from the center thereof to define a central resonant radial cavity, said tube structure having anode and cathode elements coupled to said cavity, means providing substantially parallel grid-cathode and grid-anode cavities in said casing radially externally of said tube structure, said last named cavities being annular in form and coupled to said radial cavity through the medium of said tube structure, whereby an enclosed oscillatory system is provided for applying R.F. heat directly to the center of said structure, and means for passing a body of dielectric material axially through the center of said structure to apply concentrated high frequency energy thereto within the casmg.

WILLIAM N. PARKER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,107,387 Potter Feb. 8, 1938 2,205,852 Hollmann June 25, 1940 2,227,372 Webster et al Dec. 31, 1940 2,250,096 Engbert July 22, 1941 2,284,405 McArthur May 26, 1942 2,323,201 Carter June 29, 1943 2,364,526 Hansell Dec. 5, 1944 2,370,161 Hansen Feb. 27, 1945 2,495,170 Kinn Jan. 17, 1950 2,495,415 Marshall Jan. 24, 1950 OTHER REFERENCES Marcum et al.: Heating with Microwaves, Electronics. March 1947, pages 82-85. 

